1. Field of the Invention
The present invention relates to an image processing apparatus for converting a 2D image into a 3D image, and a control method for such an apparatus.
2. Description of the Related Art
In order to create a 3D image from a 2D image, a dedicated and advanced hardware and software called a 2D-to-3D converter is used. A user is allowed to convert a 2D image into a 3D image by designating a front-and-back relationship of an object. Although this processing takes long time, it is suitable for a usage, such as a movie or the like, in which preliminary conversion is possible. In contrast, this time-consuming processing is not suitable for a usage, such as a broadcast program or the like, in which preliminary conversion is not possible and real-time conversion is required. In order to solve this problem, techniques have been proposed which are capable of converting a 2D image into a 3D image with a simple method.
JP H8-205201 A discloses a technique in which two images composed of an image for a left eye (also referred to as L-eye image) and an image for a right eye (also referred to as R-eye image) are generated by shifting a 2D image horizontally leftward or rightward, and these images are displayed alternately. A user wears liquid crystal shutter glasses so that the left eye sees only the L-eye image while the right eye sees only the R-eye image, and thus the user is caused to perceive the 2D image in three dimensions.
This related art (the method disclosed in JP H8-205201 A) will be described with reference to FIGS. 4 and 5.
FIG. 4 is a diagram illustrating a functional configuration of an apparatus for converting a 2D image into a 3D image (an image pair composed of an L-eye image and an R-eye image).
In FIG. 4, the reference numeral 111 indicates an L/R-eye image generation unit for generating two images of an L-eye image and R-eye image by shifting an input 2D image horizontally. The reference numeral 112 indicates a frame rate doubling processing unit for doubling the frame rate and outputting L- and R-eye images alternately. The reference numeral 113 indicates a display apparatus such as a LCD module. The reference numeral 114 indicates shutter glasses designed such that left and right lenses alternately let light pass through.
FIG. 5 is a diagram illustrating how a 2D image is converted into a 3D image according to the related art.
In FIG. 5, the reference numeral 121 indicates an original image, the reference numeral 123 indicates an image for a left eye (L-eye image), and the reference numeral 124 indicates an image for a right eye (R-eye image).
The L/R-eye image generation unit 111 uses an input 2D image directly as the R-eye image 124. Then, an L-eye image 123 is generated by shifting the input 2D image rightward, for example, by five pixels. In this case, the disparity between the L-eye image 123 and the R-eye image 124 is equal to a distance corresponding to five pixels.
The image output unit 112 outputs these two images (L- and R-eye images) alternately. These output images are displayed on the display apparatus 113 such as an LCD module operable at a frame rate of 120 Hz. The shutter glasses 114 controls left and right lenses (shutters) in synchronization with switching of the displayed image such that the right eye side lens lets light pass through when the R-eye image 124 is displayed and the left eye side lens lets light pass through when the L-eye image 123 is displayed. The user is thereby allowed to see the R-eye image 124 with his/her right eye and the L-eye image 123 with his/her left eye, and thus to see the 2D image in three dimensions.
A description will be made why a 2D image can be seen in three dimensions just by shifting the 2D image to the left or right direction. The 2D image 121 contains an image region which is visually in focus and an image region which is visually out of focus. The user is able to clearly perceive the shift in the horizontal direction for the image region which is visually in focus, but is substantially unable to perceive the shift in the horizontal direction for the image region which is visually out of focus. Therefore, the image region which is visually in focus seems to pop forward by the distance by which the image has been shifted, whereas the image region which is visually out of focus does not seem to pop forward so much as it has been shifted.
According to the method described in JP H8-205201 A, therefore, if an original image is an image, like a portrait, which is composed of a person which is visually in focus and a background which is sufficiently blurred, since only the person seems to pop forward, a sufficient three-dimensional effect can be obtained. However, if the original image is an image, like a deep-focus image, which is visually in focus as a whole (if the background of the original image is not sufficiently blurred), the entire image seems to pop forward, and hence the relative distance between objects that a viewer feels becomes insufficient. As a result, a sufficient three-dimensional effect cannot be obtained. In other words, the three-dimensional effect given to the viewer significantly depends on how much the original image is blurred.
JP 2000-156875 A discloses a technique in which a 2D image is created on an image creation side such that an object which is nearer to a viewer has a steeper edge, a higher contrast, or a darker color. A receiving side utilizes such information of the object image to change the shift amount in a horizontal direction between two L- and R-eye images.
According to this method, however, if the background image has a blur amount that is appropriate for providing a three-dimensional effect, the blur amount will be increased more than necessary. Thus, the quality of the image will be deteriorated by the excessive blur in the image.
Further, according to the technique disclosed in JP 2000-156875 A, it is assumed that image processing is performed on the transmission side (image creation side). Although JP 2000-156875 A describes that the three-dimensional effect can be obtained on the reception side even if image modulation is not performed on the transmission side, a similar problem to that of JP H8-205201 A described above will be posed if 2D-to-3D conversion is performed without adjusting the original image.
Further, it is assumed in the techniques described in JP H8-205201 A and JP 2000-156875 A that the focus is on an object located in front. Therefore, the front-and-back relationship between an object and a background will be reversed in an image in which the focus is on the background and the near distance is blurred.
Still further, JP 2005-136480 A discloses a method of obtaining an image with an appropriate blur amount by using two images having different points of focus from each other.
This method, however, is not able to provide an image with an adequate blur amount if only one original image is available.